Thesis (Ph. D.)--Harvard University--MIT Division of Health Sciences and Technology, 2005. / Vita. / Includes bibliographical references. / From brainstem to cortex, sound is processed in centers that are functionally and structurally distinct. In animals, invasive electrophysiology and histology has revealed these distinctions and, consequently, organizational principles behind sound processing. In humans, however, comparable demonstrations are sparse. This thesis presents three MRI studies that provide new information regarding structural and functional distinctions between auditory centers in living humans. The first study compared the effect of a fundamental acoustic variable, sound level, on the population neural activity of auditory brainstem, thalamus and cortex. Brainstem and cortex exhibited contrasting sensitivities to sound level (growth in activation followed by saturation in brainstem vs. plateau then growth in cortex), with thalamus showing intermediate properties. The second study identified functional distinctions between cortical areas by spatially mapping the temporal properties of fMRI responses. Using a continuous noise stimulus, we found sustained responses on Heschl's gyrus flanked medially and laterally by more phasic activity. This pattern suggests that transient activity marking the beginning and end of a sound is most pronounced in non-primary areas of auditory cortex. The region of sustained responses may correspond to primary and primary-like areas. Thus, it may present a physiological marker for these areas in neuroimaging studies, something that has long been needed in the auditory neuroimaging field. The third study examined whether auditory cortical areas can be distinguished - in the living human brain - based on classical features of cortical gray matter previously resolvable only in postmortem tissue. / (cont.) By mapping the imaging parameter R1, we identified regions of heavily myelinated gray matter that may correspond to primary auditory cortex. We further found greater gray matter myelination of the left temporal lobe, which may be a substrate for higher fidelity temporal processing on the left, and for left-hemispheric speech and language specializations. Being able to resolve gray matter structure in-vivo opens the way to relating cortical physiology and structure directly in living humans in ways previously possible only in animals. / by Irina S. Sigalovsky. / Ph.D.
| Identifer | oai:union.ndltd.org:MIT/oai:dspace.mit.edu:1721.1/30272 |
| Date | January 2005 |
| Creators | Sigalovsky, Irina S., 1972- |
| Contributors | Jennifer R. Melcher., Harvard University--MIT Division of Health Sciences and Technology., Harvard University--MIT Division of Health Sciences and Technology. |
| Publisher | Massachusetts Institute of Technology |
| Source Sets | M.I.T. Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 144 p., application/pdf |
| Rights | M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission., http://dspace.mit.edu/handle/1721.1/30272, http://dspace.mit.edu/handle/1721.1/7582 |
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